Oil and gas companies pursue to an ever increasing degree more functionality in wells, both land/platform and sub sea wells. The trend to implement multilateral capability (several well trajectories kicked off from a single drilling point and producing through the same well head (valve tree) is particularly determined. This approach to well completion requires means to close and open remotely the valves (sliding sleeves) isolating and connecting the various laterals with the main bore. For some completions choke valves could also be required. Further, down-hole production equipment, such as separation equipment, is required in some wells and may require remote control functionality. For all of these functions automatic, remote control is desirable, such as to prevent costly re-entry into the well. Due to space constraints in the tubing hanger area of a well, which limits the number of penetrations for electrical wires and hydraulic conduits, such remote control systems are required to be based on some form of multiplexing. Also, running a tubing string with a large number of cables/tubes in the annulus can be cumbersome and time consuming.
Several contractors have developed multiplexed control system for down-hole applications, mostly based on high temperature electronic circuitry designed and supplied by major international corporations especially for operation in hot environments. Such systems have achieved various degrees of success. However, all electronic circuitry have similarity in failure mechanisms and patterns, inherent in semiconductor devices. One characteristic is that it is impossible to predict the failure time of a given circuit. The failure of electronic circuitry tends to follow statistical models, inferring that some circuits may fail early and some (most) may perform fault free for many years.
This failure pattern is unfortunate in a down-hole application where the robustness of mechanical equipment with the inherent failure modes of mechanical components have demonstrated success as opposed to electronic circuitry which is still in the maturing process. Correctly designed and installed mechanical components will normally function for a period of time determined by wear, corrosion or erosion, depending on use and exposure.